The present invention relates generally to printing presses and more particularly to a device and method for driving rolls and cylinders in a printing press.
Offset lithographic printing presses typically have a plate cylinder carrying an imaged plate. During printing, the plate is inked, and the inked image is transferred to a blanket which then contacts paper sheets or a continuous web of paper. Ink for the plate cylinder may be provided via an inker including an inker cylinder in rolling contact with the plate cylinder.
The drive for an offset lithographic printing press traditionally has included a common drive shaft running on a gear side of the printing press, with several printing units of the printing press engaging the shaft with worm gears and other gears to derive power from the shaft.
Shaftless drive configurations for lithographic offset printing presses use direct or indirect drive motors, which supply the necessary driving forces to the plate and/or blanket cylinders using one to four motors. The inker may be geared to the plate cylinder or may be driven by a separate or additional motor. Shaftless printing presses are described, for example, in U.S. Pat. Nos. 6,216,592 and 5,979,317.
Commonly-owned U.S. Pat. No. 6,050,185, hereby incorporated by reference herein, purports to disclose a shaftless drive with a first drive motor driving a first inker roller either directly or via a further drive. The first drive motor is mechanically coupled to the first plate cylinder via a first gear train, which may include a gear wheel mounted to the drive shaft of the first plate cylinder. A second drive motor drives another plate cylinder and inker roller. The first blanket cylinder and the second blanket cylinder of the press are mechanically coupled to one another and are driven by a third drive motor.
European Patent Application No. 0 699 524 purports to disclose an offset printing machine. Cylinder and functional groups are driven with minimum technical requirements. A printing unit is provided where the plate cylinders are each driven by a separate electric motor and are not mechanically coupled to each other. Independently driven cylinders in a folder are also disclosed.
Japanese Patent No. 212 00 48 purports to describe an ink roller driving device of a printer that intermittently rotates an ink main roller, swings or rotates a doctor roller and reciprocates ink reciprocating rollers with a driving motor.
U.S. Pat. No. 6,408,748 purports to describe using separate electric motors to drive inking and form or blanket cylinders of a printing unit.
Commonly-owned published U.S. patent application Publication No. US 2002/0096066, which is hereby incorporated by reference herein and related European Patent Application 1 226 937 A1, purport to disclose a shaftless motor drive for a printing unit having two inkers and two motors, each motor being directly connected to one of the two inkers.
An object of the present invention is to provide a printing unit useable in a shaftless offset printing press.
An additional or alternate object of the present invention is to provide a printing unit having a gear train that is driven from the drive gear of an inker rather than by one or more gears of the plate or blanket cylinders.
A further additional or alternate object of the present invention is to provide a simple and effective solution for positively and accurately driving the cylinders of a printing unit so as to provide sufficient static gear preload and to avoid gear train backlash.
The present invention provides a printing unit that includes a first plate cylinder, a first blanket cylinder for selectively contacting the first plate cylinder, a first inker for inking the first plate cylinder, a second plate cylinder, a second blanket cylinder for selectively contacting the second plate cylinder, and a second inker for inking the second plate cylinder. The printing unit also includes a first inker drive gear connected to the first inker for driving the first inker, and a motor uniquely associated with the printing unit and configured to drive the first inker drive gear. The printing unit also includes a gear train engaging the first inker drive gear and being driven by the first inker drive gear so as to drive the first plate cylinder, the first blanket cylinder, the second blanket cylinder, the second plate cylinder and the second inker.
Using the inker drive gear to drive the entire gear train provides a driving point that is removed from the blanket and plate cylinders, allowing more space adjacent those cylinders for other desired components. This can be particularly advantageous, for example, for printing units with mechanisms attached to the plate cylinders or their gears for providing lateral and circumferential registering. The register mechanism may limit drive access to the plate cylinder gear. In addition, the axes of the plate and/or blanket cylinders may shift position slightly when the printing unit is taken off impression, which can be an additional problem if the drive point is attached to one or more of these cylinders. Moreover, the present invention provides an inexpensive solution to the problem of converting certain existing shaft driven presses with minimal modification of the existing gear train, particularly when the shafted presses are inker driven.
According to the present invention, the motor may directly engage the first inker drive gear, and may include a pinion for providing the engagement. The first inker drive gear may have a single teething that engages both the motor and the gear train, or may be a compound gear having a first teething engaging the motor and a second teething engaging the gear train. As used herein xe2x80x9ccompound gearxe2x80x9d may be a single-piece gear having a plurality of teethings, or may be a plurality of gears connected to each other, such as by being mounted to a common shaft. Other variations for driving the first inker drive gear are also possible.
Preferably the gear train includes: a first plate drive gear driving the first plate cylinder and engaging the first inker drive gear; a first blanket drive gear engaging the first plate drive gear and driving the first blanket cylinder; a second blanket drive gear engaging the first blanket drive gear and driving the second blanket cylinder; a second plate drive gear engaging the second blanket drive gear and driving the second plate cylinder; and a second inker drive gear engaging the second plate drive gear and driving a second inker cylinder. Preferably, the first and second plate drive gears and the first and second blanket drive gears each drive a respective cylinder by being rigidly attached to an axle of the respective cylinder.
The gear train may include a plurality of gears, each associated with one of the first and second blanket cylinders, the first and second plate cylinders, and a cylinder of the second inker. Preferably, each of the blanket and plate drive gears in the gear train have a diameter equal to the diameter of the cylinder with which it is associated. Most preferably, the gears of the gear train all have the same diameter, thereby improving drive characteristics.
The present invention also provides a method of driving a printing unit. The method includes driving a first inker drive gear using a motor uniquely associated with the printing unit, driving a first inker connected to the first inker drive gear using the first inker drive gear, and driving a first plate cylinder, a first blanket cylinder, a second blanket cylinder, a second plate cylinder and a second inker using a drive train, the gear train engaging and being driven by the first inker drive gear.